Pneumatic tires holding air are mounted on wheels of automobiles or bicycles. Even if air is pumped into such a pneumatic tire until the air pressure therein reaches a specific level, the air gradually escapes therefrom and the air pressure therein gradually decreases over time. When the air pressure is too low, it adversely affects the ride quality or handling. Thus, when the air pressure becomes much lower than the a specific level, air should be supplied into the pneumatic tire with an air supply device such an air pump.
However, a considerable force is required to operate an air pump to feed air into a pneumatic tire. Thus, it is difficult for a person without much strength to operate an air pump to feed air into a pneumatic tire.